Semiconductor Lasers and Laser Dynamics XII

Mode-locked laser diodes (MLLDs) are at the heart of ultrafast laser science, generating laser pulses that can be harnessed for emerging technologies. In this study, we explore a two-section InGaAsP/InP quantum well laser (840 μm length, λc = 1570 nm, 50 GHz internal roundtrip frequency) with a single-side antireflection coating in a tunable 15 cm external cavity with a 1 GHz repetition rate. Compared to our previous monolithic operation, clean passive mode-locking was achieved, yielding pulse durations below 1.37 ps at 100 mA gain current and −0.8 V absorber bias under a 20 m SMF-28 dispersion-compensating scheme. We demonstrate that self-mode locking in this external cavity configuration is also possible and significantly enhanced when the combined system cavity lengths are chosen in specific ratios and a flexible external cavity allows for precise tuning for sub-picosecond pulse formation. These findings point to the potential utility of the system in ultrafast terahertz spectroscopy with variable repetition frequency.

In this work, we present a versatile and agile optical frequency comb source based on a semiconductor quantum-dash mode-locked laser dynamically controlled through phase-tuned optical feedback. By exploiting ultrashort optical feedback paths, we achieve control over the comb characteristics, enabling simultaneous spectral broadening and tunable control of the optical spectrum and repetition frequency. With this approach, we achieve significant spectral broadening (from 13 nm to 33 nm) and demonstrate dynamic tuning of the repetition rate over a range exceeding 200 MHz.

This talk reports advances in free-space ultrafast mid-infrared modulators exploiting strong light–matter coupling. Operating at room temperature, these devices achieve > 80 % modulation contrast and -3 dB cutoff frequencies up to 15 GHz around 9 μm wavelength. When driven by short (~100 ps) electrical pulse trains, from a single or dual pulse generator, these modulators enable the generation of single- and dual “electro-optic” frequency combs. The accessible bandwidth is up to 20 GHz, with mode spacings down to 10 MHz (limited by the pulser). We perform a proof-of-concept dual-comb spectroscopy experiment using a single modulator and a single quantum cascade laser with a NH₃ cell and a Ge etalon. The results reveal that high-performance mid-IR modulators could be suitable for spectroscopy, frequency comb generation and, in the long term, spatial light modulation.

We report the controlled generation of optical frequency combs with rational subdivisions of the gain switching modulation frequency in a monolithically integrated, mutually coupled semiconductor laser system operated under symmetric biasing. Under symmetric biasing, the device can exhibit period doubling and period tripling dynamics that produce comb spacings equal to one half, one third, and two thirds of the modulation frequency respectively. A delay differential rate equation model incorporating phase noise reproduces these bifurcations and identifies clear regions of stable subharmonic operation with broad regions of optical chaos also present. The observed states are robust to variations in modulation and injection conditions. This work expands the functionality of symmetrically coupled gain switched lasers and enables compact, tunable on-chip frequency division for applications in optical communications.

Vertical-cavity surface-emitting lasers (VCSELs) dominate optical short-haul communication systems; however, recent studies have demonstrated that spin-VCSELs offer distinct advantages over their conventional counterparts for ultrafast optical communication. To date, research on spin-VCSELs has been restricted to the single-mode regime, while the inherently multimode nature of VCSEL operation has remained unexplored. In this work, we present an experimental investigation of multimode polarization dynamics in spin-VCSELs operating in multiple transverse modes. These measurements show polarization oscillations of the multimode regime, which have not been previously observed. Furthermore, we introduce an extended theoretical framework based on the classical spin-flip model, generalized to account for an arbitrary number of transverse modes. Using this model, we demonstrate that under specific conditions, the modulation bandwidth can be enhanced, thereby surpassing the single-mode performance limit.

We demonstrate nanosecond-scale discrete wavelength switching in dual-wavelength lasers monolithically integrated on InP with an electro-optically phase-controlled feedback cavity. Experimentally, transition times as short as 1.24 ns are achieved, with faster switching for stronger optical feedback and larger modulation amplitudes, and minimal sensitivity to gain differences. Using a multi-mode Lang–Kobayashi model, simulations confirm these trends, clarify the role of the mode-coupling parameter, and reveal trade-offs between switching speed and side-mode suppression. These results highlight the potential of integrated multi-wavelength lasers for compact, high-speed all-optical switching.

We demonstrate a compact all-optical wavelength conversion scheme based on optical injection into a feedback-controlled InP multi-wavelength laser (MWL) integrating a single gain section and an on-chip feedback cavity. Our laser-assisted cross-gain modulation (LA-XGM) approach enables data transfer between intrinsic laser modes without requiring external probe lasers. We achieve wavelength conversion of on–off keying signals up to 10 GBd over a 1.3 THz range, with agile output wavelength and even multi-wavelength broadcasting. This integrated and energy-efficient method offers a scalable solution for agile, reconfigurable WDM and optical switching applications.

We present an experimental study of an optically spin-injected spin-VECSEL, based on a ½-VCSEL structure in a VECSEL architecture. The coupling constant of the structure has been found to be very close to 1 for circular polarizations, which is optimal for spin-laser applications by minimizing the spin unbalance required for polarization switching. In our experiment, the active medium is pumped by a dual-pump architecture. The first one allows the threshold to be reached, while the second one allows fast electronic spin injection. Moreover, an electro-optic plate which compensate the residual linear birefringence, is placed in the VECSEL cavity in order favor polarization switching. In this way, the polarization dynamic behavior of the spin-VECSEL is studied under different spin injection frequency modulations.

We investigated noncircular-aperture VCSELs as potential broadband nonlinear elements for optical neural networks. The devices consist of two connected mesas sharing common electrodes, where optical injection into one mesa can redistribute emission to the other. Measurements of emission characteristics under varying optical injection powers and frequency detunings revealed a stable response over a broad detuning range (20 GHz). This broadband nonlinear behavior highlights the suitability of coupled-mesa VCSELs as nodes in optical neural networks, offering robustness against wavelength variations across VCSEL arrays.

Climate change is one of the greatest and most urgent challenges of our time. If we want to keep the planet livable, greenhouse gas emissions must be net zero by 2050. Food production is responsible for up to a staggering 34% of greenhouse gas emissions. At the same time, our food production is highly sensitive to climate change and this is already having a major impact on the food system, such as crop failures due to extreme weather conditions. As a result, food security and food sustainability are top of mind. Technology can and will make the difference. The unprecedented convergence of AI, gene editing, DNA synthesis and biotechnology will revolutionize global industry, particularly in the agrifood domain. This presentation will show how optical sensing in general and photonic integrated circuits in particular are unique and indispensable technologies that provide solutions for farmers, food processing industry and consumers, and will help guide the transition of our food ecosystem to a more secure and sustainable industry. New tools in barns, in greenhouses, in orchards, in protein bioreactors and the accompanying digital twin AI technology will be shown.

Spectral imaging has long promised to uncover physiological and molecular information invisible to the human eye. Yet, despite decades of innovation, its translation into clinical routine has been slow. Beyond regulatory hurdles, challenges such as ill-posed inverse problems, data scarcity, and the demand for real-time analysis have repeatedly stalled progress. In this keynote, I will present recent breakthroughs at the intersection of computational biophotonics and machine learning that are reshaping the field. I will discuss how we combine spectral imaging with deep learning to achieve real-time tissue characterization in surgery and intensive care. Case studies will illustrate how spectral imaging can enable context-sensitive, clinically actionable support during interventions, transforming invisible spectral signatures into robust biomarkers. I will highlight not only our successes but also the failures that have shaped them. From spectral unmixing approaches that collapsed under distribution shifts to algorithms that failed spectacularly in the operating room, I will show how negative results became the foundation for new strategies. By dissecting what went wrong, we discovered how to adapt models across species and sensors, quantify uncertainty in predictions, and build validation frameworks that hold up under clinical reality. By putting the spotlight on failure—and how it fuels methodological innovation—I will argue that embracing negative results is the key to moving spectral imaging, powered by AI, from promise to practice. The future of the field may not depend on avoiding failure, but on failing better.

We report RF-injection-locked quantum-cascade vertical-external-cavity surface-emitting lasers (QC-VECSELs) operating in the THz regime. By injecting RF signals at the cavity round-trip frequency as well as at harmonic and sub-harmonic orders, the device produce stable, evenly spaced multimode emission with bandwidths exceeding 300 GHz. Owing to the fast saturable gain of QC active region and the absence of spatial hole burning in the external-cavity geometry, the platform enables the realization of Quantum-Walk (QW) combs using strong RF modulation. Distinct on- and off-resonance behaviors are observed, demonstrating QC-VECSELs as a versatile and tunable source for broadband THz frequency-comb generation.

The mid-infrared spectral region hosts fundamental molecular vibrations, enabling label-free chemical detection. Wavelength-tunable quantum cascade lasers (QCLs) suit mid-IR spectroscopy with high power, high spectral resolution, small footprints, and excellent beam quality. Integrating QCLs with MOEMS grating scanners in external cavities yields compact, rugged modules with exceptional tuning speed and broad spectral coverage. Merging QCLs with MOEMS grating scanners in an external cavity provides very compact, rugged modules. In this contribution, we will give an overview of our current efforts towards automated assembly of our resonant MOEMS-EC QCL modules, simplifying the assembly process and making it more suitable for volume production at reduced costs. Furthermore, we showcase a four-core module, in which we combine four broadband resonant MOEMS-EC-QCLs into a single output beam and are able to measure the combined IR spectrum of all lasers in only 0.5ms.

We demonstrate advanced control capabilities in a fully integrated optical frequency comb platform featuring THz ring quantum cascade lasers by exploiting external RF modulation resonant to the fundamental cavity round-trip frequency and its subharmonics. We present a monolithic higly-tunable optical frequency comb source featuring a planarized double-ring THz quantum cascade laser with surface-emitting bullseye antenna. The device operates as single-mode in free-running around 3.0 THz and as a quantum walk comb source when applying external RF modulation resonant to the cavity roundtrip frequency (frt). We observe spectral broadening injecting at finj=frt~15.9 GHz, with the maximum bandwith growing with the injected power up to ~500 GHz. The coherence of the comb states is confirmed by SWIFT measurement. A similar broadening occurs when the injected RF frequency is swept around subharmonics of the fundamental round-trip frequency. The mode spacing follows the injected frequency and SWIFT analysis confirms the coherence of these new comb states, down to frt/10~1.59 GHz. Subharmonic injection enables the use of two-tones modulation techniques for spectral shaping of the optical frequency comb, overcoming the limitations imposed by RF components.

Optical injection (OI) is a well-established technique for stabilizing laser frequency and linewidth or for inducing nonlinear dynamics. When optical feedback (OF) is added, the injection-locking (IL) region is strongly modified and richer dynamics emerge. While theory predicted that OF can induce an oscillatory IL boundary, this had not been confirmed experimentally. We report the first experimental observation of a quasiperiodic cascade in a laser diode under simultaneous OI and OF. The feedback delay (τ = 0.5 ns) corresponds to an external-cavity frequency of 2 GHz. As the injection frequency is tuned, the laser alternates between periodic and quasiperiodic regimes, in excellent agreement with recent numerical predictions [1]. Two distinct scenarios arise depending on whether the feedback operates in the short- or long-cavity regime. These results provide experimental evidence of feedback-induced cascades and clarify the complex boundaries of injection locking in semiconductor lasers. [1] Oliverio, Rontani & Sciamanna, Opt. Express 32, 25906 (2024).

The Lang-Kobayashi equations are the standard tool for modelling lasers subject to external feedback from a regular mirror. When the feedback comes from a fibre Bragg grating (FBG), present modelling requires a computationally expensive convolution term, which provides limited analytical insight into the system’s behaviour. We present a novel modelling approach that approximates FBG feedback using discrete delay terms, avoiding the need for numerical convolution while preserving the essential physics. This enables analysis of mode structure and solution stability, providing a bridge between numerical simulation and analytical understanding.

The advancement of narrow linewidth lasers in the visible spectrum is essential for various applications, including laser cooling, atomic clocks, and gas sensing. We report a fiber Bragg grating (FBG) external cavity GaN DFB laser diode emitting at 452 nm with unprecedented narrow linewidth performance. The injection locking scheme reduces the intrinsic linewidth from ~ 1 MHz to 170 Hz, corresponding to nearly 40 dB of noise reduction. The integrated linewidth over a 10 ms time interval is roughly 100 kHz. This approach opens a path toward an integration in a compact package.

Passively mode-locked lasers subject to feedback from an optical external cavity can have relatively small long-term timing jitter if the delay is chosen resonant to the repetition frequency. Despite this positive effect of the feedback, it also induces large timing fluctuations on short time scales. Consequently, the commonly used von Linde and Kéfélian techniques of experimentally estimating the timing jitter can lead to large errors in the estimation of the arrival time of pulses. Adding a second feedback cavity of the appropriate length can significantly suppress the noise-induced modulations induced by the first feedback cavity. With our double delay approach we can thus reduce both, short time-scale fluctuations of the interspike interval time and the variance of the fluctuation of the pulse arrival times on long time scales.

Traditional photonic crystal surface-emitting lasers (PCSELs) rely on isolated quasi-bound states in the continuum (q-BIC) that are generally at the center of the Brillouin zone and which offer high directionality and quality factors. However, due to the isolated nature of the q-BICs they rely on, PCSELs are fundamentally limited in applications that demand continuous tunability, requiring the construction of many different PCSELs that are switched on and off to achieve such tunability. Here, we introduce a new cavity geometry that uses a novel polarization- and angle-selective Bragg reflector to develop a surface emitting laser that features a continuous line of bound states in the continuum. The resulting dispersion allows for high-Q lasing states across a broad wavevector range, with the potential for twin-beam emission whose angular separation can be tuned by adjusting the temperature and injection current into the quantum well gain medium. Numerical simulations confirm that this configuration yields a high-quality factor and supports single-mode operation over large areas due to its reduced density of resonances. The approach will not only enable continuous angular beam control but also offers compatibility with existing fabrication methods. Our study represents a significant step toward overcoming the limitations of isolated-q-BIC-based devices and opens new possibilities for dynamic and tunable beam-steering in integrated photonics. Acknowledgement: SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Energy-efficient and compact on-chip light sources are essential for the development of optical interconnects in data centers. In this work, we present an electrically driven one-dimensional photonic crystal nanobeam laser featuring a novel “butterfly-wing” design that enhances carrier injection efficiency and enables directional outcoupling into an integrated waveguide. We employ a lateral current injection scheme and a high Q-factor cavity design featuring an asymmetric mirror configuration to achieve effective coupling into the waveguide. The active region consists of a 6.16 μm long, 5 quantum well buried heterostructure embedded in the defect region of the photonic crystal. We demonstrate lasing operation with a threshold current of 416 μA, confirmed by linewidth narrowing and single-mode operation. This work demonstrates a promising platform for efficient, compact light sources suitable for on-chip optical communication.

We would like to present our work on optimising an InGaAs QW VECSEL for emission at around 775 nm. Increasing the Indium content of our GaInP barriers enables absorption of a 675 nm pump laser, resulting in an increased efficiency compared to a 532 nm pumped VECSEL. To further increase the output power, a multi modal cavity setup was chosen.

We report, to the best of our knowledge, the first flip-chip-integrated extended-cavity laser operating at 637 nm on a silicon-nitride (SiN) waveguide platform, achieving an on-chip output power of about –5 dBm and a wavelength tunability of 4 nm. The device integrates a reflective semiconductor optical amplifier (RSOA) with a wavelength-selective feedback circuit formed by paired ring resonators in Vernier configuration on a SiN-based photonic integrated circuit (PIC). The RSOA is bonded onto the PIC through a passive pick-and-place process, forming a compact extended cavity defined by the RSOA’s back facet and an on-chip reflector. RSOA’s light is coupled into a multimode edge coupler that maintains efficient coupling despite lateral misalignments of ±2.4 µm with a 1 dB penalty, while vertical alignment accuracy is ensured by etched pedestals beneath the RSOA. The paper discusses the device design and characterization results, confirming the feasibility of visible-wavelength ECLs realized through flip-chip integration.

In emerging optoelectronic systems designed for AI and neuromorphic integration, group-IV photonics and particularly (Si)GeSn-based lasers are of significant importance due to their CMOS compatibility and potential for scalable, on-chip optical interconnects. Towards further improvement of material and device, here we investigate self-heating in a state-of-the art continuous-wave (Si)GeSn microdisk laser using stroboscopic full-field X-ray diffraction microscopy with 10 ns temporal and 150 nm spatial resolution. This study quantifies and visualizes heating induced by the electrical pumping pulses, revealing contact-dominated Joule heating as the primary cause of dynamic temperature changes in the device. Moreover, we confirm that heat localized at the contact region does not effectively propagate into the active lasing layer due to the low thermal conductivity and high heat capacitance of the SiGeSn/GeSn multi quantum wells. These finding are valuable in guiding future thermal design of group-IV photonic devices.

The growing demand for high-speed optical data transmission in data centers necessitates VCSELs with higher modulation bandwidths. Conventional VCSELs are limited by the relaxation oscillation frequency, restricting performance to about 35 GHz. Coupled cavity VCSELs (CC-VCSELs) overcome this limitation by forming optical supermodes that introduce additional resonances and extend the modulation bandwidth beyond conventional designs. Another promising approach is the spin-polarized VCSEL (Spin-VCSEL), where the emitted polarization is governed by carrier spin dynamics, enabling operation frequencies exceeding 200 GHz and potential data rates beyond 240 Gbit/s per channel. Combining both CC-VCSEL and Spin-VCSEL concepts offers a highly promising route toward further bandwidth enhancement. This work presents birefringence measurements of circular and bow-tie CC-VCSELs using a rotating half-wave plate, linear polarizer, and high-resolution optical spectrum analyzer, providing a foundation for future studies on spin injection and polarization dynamics in coupled cavity structures.

I review the use of large-area VCSELs in neuromorphic computing and I explore the prospects of co-integration with linear PICs for scalable photonic integrated computing systems.

This work experimentally demonstrates a fiber nonlinearity compensation technique by using the deep photonic reservoir computer (PRC). The deep PRC is constructed by cascading injection-locked semiconductor lasers with optical feedback. The deep PRC has 3 reservoir layers and a total of 120 virtual neurons. The operation frequency of the deep PRC is as high as 20 GHz. The signal under processing is a 240 Gbps 16-QAM coherent signal, with a launch power of 12 dBm and a transmission distance of 50 km. It is experimentally proved that the deep PRC achieves a Q-factor gain as high as 0.58 dB, compared with the conventional digital signal processing technique.

We present a physical, optical simulated annealing set-up used to solve for the ground state of the Ising Model. The annealer can map exactly to the Glauber Dynamics, a Monte Carlo method known to describe the evolution of spins in the Ising Model, with the sampling step performed by an excitable integrated photonic device, removing some costly digital calculations. The system has been shown to solve benchmark graphs. There is also room for improvement in the digital components and potential for parallel sampling using multiple lasers on the same compact photonic chip.

We investigate synchronization in an all-to-all coupled semiconductor laser (SL) network with optical feedback. Through combined numerical and experimental studies, we characterize the network dynamics under frequency detuning, coupling delay mismatches, and parameter heterogeneities. Using a four-node polarization-maintaining fiber-coupled system with very low lasing threshold lasers for improved power efficiency, we control coupling strength and laser detuning to tune the network’s synchronization and nonlinear responses. Numerical simulations incorporating measured heterogeneities reveal chaotic synchronization with cross-correlations up to 0.9. Experiments also reveal cross-correlations between SL pairs of up to 0.9. These findings demonstrate that controlled coupling and frequency detuning enable high synchronization and diverse dynamics, validating semiconductor laser networks as promising hardware substrates for neuro-inspired information processing applications.

Synchronization of semiconductor lasers is often hindered by their frequency differences and strong amplitude–phase coupling. Previous schemes for laser synchronization are mostly based on homogeneous coupling among the lasers, i.e., the coupling of one laser to other lasers is identical for every laser. We propose to overcome intrinsic disorder in lasing frequencies with tailored disorder in coupling strengths. In particular, the coupling strength between any pair of lasers scales with their frequency difference. We realize this approach experimentally with three single-mode vertical cavity surface emitting lasers (VCSELs) and use a spatial light modulator to control the coupling between the lasers. The critical coupling threshold for frequency locking of three VCSELs is significantly lower than that with uniform all-to-all coupling, and stable phase locking is observed over a wider range of coupling strength. Our method provides an efficient and scalable route toward large-scale synchronization of semiconductor lasers.

Mutually coupled single-mode laser diodes are investigated to yield extreme events. While the two lasers are found to be mutually locked into continuous-wave emissions of constant intensities, occasional interruptions by unlocking yield strong pulses in an intermittent manner. The high relative occurrences approaching 1% are attained for generating strong microwave pulses with intermittent timing. On one hand, the extreme events are investigated via the equivalent space-time maps in observing their emergences, thereby disclosing the physical mechanisms for their stochastic formation across consecutive round trips through the antiguidance effect of the injected lasers. On the other hand, the timing information related to their occurrences is analyzed with particular attention on identifying a Poisson process instead of a log-Poisson process. The resultant generation of microwave pulsations with widths of the order of 100 ps and amplitudes exceeding 6 times the standard deviation are potentially applicable to wireless propagation in the Ku band.

Semiconductor lasers subject to external optical injection and current modulation exhibit a wide range of nonlinear behaviors, including phase locking, quasiperiodicity, and fully developed chaos. Ιdentifying the boundaries between these regimes is essential for understanding the onset of broadband chaotic emission and for applications such as secure communications, sensing, and high-rate chaos-based signal generation. In this work, we investigate the dynamical complexity of a directly modulated, optically injected semiconductor laser using permutation entropy (PE) applied to both the full rate-equation model and a reduced one-dimensional Poincaré phase map. PE provides a model-free quantifier of temporal complexity that readily distinguishes regular, quasiperiodic, and chaotic dynamics. By constructing PE-based resonance diagrams across a broad range of modulation amplitudes and detuning fractions, we show that the reduced phase map accurately reproduces the global organization of complexity observed in the full system, including the high-entropy regions emerging at the intersections of Arnol’d tongues. Representative cases demonstrate close qualitative agreement between the two descriptions, while also revealing systematic quantitative offsets associated with the higher intra-cycle variability present in the full intensity waveform. These results demonstrate that permutation-entropy analysis, combined with phase-map reduction, offers an efficient framework for mapping and interpreting the complexity landscape of modulated optically injected semiconductor lasers, enabling rapid exploration of parameter spaces relevant to chaos-based photonic applications.

Pulsing laser systems of different type produce periodic trains of short pulses, which are finding increasing applications across multiple areas of technology. For example, they form the basis of optical frequency combs, which enable precision time and frequency measurements with accuracies surpassing the best atomic clocks. However, what happens to the response of a pulsing laser when it experiences discrete and strong perturbations, such as sudden power fluctuations? We consider a system of two coupled Van der Pol oscillators as a prototypical case study and investigate the geometric mechanisms that control its response to increasingly stronger perturbations. We explain how the response depends on the phase in the pulse train at which such perturbations are applied.

Vertical-cavity surface-emitting lasers (VCSELs) can exhibit chaotic dynamics even in free-running operation due to mode competition. While most studies have focused on single-mode VCSELs, we numerically investigate multimode VCSELs including higher-order transverse modes. The emergence of these modes introduces additional bifurcations at higher pump currents, producing complex dynamics and polarization mode competition consistent with recent experiments. We show that the chaotic dynamics originates from the interplay between the undamped dynamics at the relaxation oscillation frequency and the self-pulsation at the birefringence frequency. Furthermore, we observe a novel dynamic termed transverse mode hopping (TMH) where different transverse modes with the same polarization exhibit a strongly anticorrelated dynamics. Interestingly, under certain conditions, the multimode VCSEL exhibits less complex dynamics than the single-mode one, even reaching a stationary state after a chaotic regime. Our numerical findings are in good qualitative agreement with recent experiments.

Raman distributed optical fiber sensing enables long-range temperature monitoring, yet its performance is limited by weak Raman backscattering and the bandwidth of practical detectors. We experimentally demonstrate a chaos-based Raman sensing scheme using a bandwidth-tailored chaos laser, where a fiber Bragg grating (FBG) shifts the spectral centroid from 6 GHz to 600 MHz and increases the chaos energy within the APD bandwidth from 0.4% to 32%. With stronger Raman backscattering, the SNR of the cross-correlation peak reaches about 7.5 dB, representing a 4 dB improvement compared with the non-tailored chaos source. To stabilize the demodulated position under finite sampling, we further implement the Spline interpolation to sharpen the correlation trace and achieve a temperature-anomaly localization precision at the sub-centimeter level.

Chip-scale optical frequency combs have emerged as a promising approach towards compact and efficient light sources that provide a multitude of tones for parallel WDM transmission, spectroscopy, LiDAR or microwave photonics. Among various technical approaches, monolithic semiconductor mode-locked lasers stand for their compact chip design, low power consumption, wide optical bandwidth, low phase noise, and the ability to generate ultra-short pulses. In this talk, we will focus on quantum-dash based devices, and present photonic stabilization schemes that improve correlation between comb lines together with enlarging the optical bandwidth. Finally, we will demonstrate their capability to achieve over 10 Tb/s optical communication, highlighting their potential for the next-generation photonic systems.

Processing high-frequency signals requires high-bandwidth electronic ADCs; however, in this abstract, we employ a quantum-dot mode-locked laser (QD-MLL) for radio-frequency downconversion to avoid this requirement. We report the successful down-conversion of a 400-MHz-spaced multi-tone signal from 60 GHz to 20 GHz, achieving an electrical signal-to-noise ratio of 30 dB.

Our study focuses on the transfer of coherence through the optical injection of semiconductor distributed feedback (DFB) lasers. We use master lasers with linewidths ranging from millihertz to megahertz. The significant disparity in linewidth between the master and slave lasers allows us to examine the effect of coherence on frequency locking. Our experimental results demonstrate that frequency locking depends on the properties of frequency noise. For instance, the minimum optical power required to achieve frequency locking also depends on these noise properties. This study sheds new light on coherence-transfer dynamics in systems with an extreme linewidth mismatch. It also paves the way for the development of compact, low-noise, frequency-stable semiconductor laser sources for advanced photonic applications.

Coherent and narrow-linewidth OFCs can serve as independent lasers for ISAC systems supporting both DAS systems and coherent optical communications in WDM links. In this study, we investigate the effects of cascaded injection locking in a two-stage optical injection system. The cascaded injection locking effectively stabilizes Phase-Locked Period-One-based OFC (PPOFC) signals with at least 10 coherent comb lines, each exhibiting an optical linewidth of less than 10 kHz. Furthermore, each comb line of the PPOFC signals can function as an independent laser for a DAS system, enabling the retrieval of driving acoustic waves with a SNR greater than 30 dB.

Quantum-enhanced imaging is an emerging area of research with relevance to a wide variety of application areas, including transport, gaming, environmental research, and security and defence. This subject encompasses a range of techniques and utilizes a number of developing quantum technologies. Time-resolved single-photon imaging approaches have been used to reconstruct high-resolution three-dimensional images, including challenging scenarios such as imaging through atmospheric obscurants and clutter. Critically, this approach has been extended to imaging in turbid underwater conditions. In the past, image reconstruction often proved to be time-consuming due to the inherent computational complexity, however advances in algorithms and hardware have allowed examples of “real-time” reconstruction of moving targets. Single-photon imaging has been used in demonstrations of moving target identification and human activity recognition with the aid of artificial intelligence approaches. Alternative single-photon imaging approaches, such as ghost imaging, will also be discussed.

I will present the PIXEurope Pilot Line, a recently started 400MEuro initiative under the Chips JU, that aims at developing and transferring advanced photonic integrated circuit (PIC) technologies and processes. Through Open Access, PIXEurope will support end-users in increasing the readiness level of their products. I will also present some technologies, leveraging PICs, that were developed at ICFO and transferred to spin-offs, now commercializing quantum random number generators, cryptography systems and phase imagers. Biography: Valerio Pruneri is an ICREA Professor and Corning Inc. chair, leading the Optoelectronics group at ICFO. He is also the Director of PIXEurope Pilot Line. Previously he worked for Avanex, Corning, Pirelli, and the University of Southampton. With his groups in academia and industry, he has developed technologies for the photonic, photonic integration, and quantum. He is inventor in more than 70 granted or pending patent families, leading to numerous industrial collaborations and the creation of four spin offs, Quside, Sixsenso, Luxquanta and Shinephi.

We propose a 1D topological phase-twist laser, in which each air hole in a triangular lattice is defined by the phase angle of its position vector with respect to the lattice center, designated as the origin. The Kekulé phase is then modulated to introduce a branch cut with twisted local phases, resulting in a phase-singularity point at the center. This singularity helps to create a topologically protected defect in the lattice, supporting a robust bound mode that physically originates from the Jackiw-Rebbi solution. Unlike previous TLs reported in the literature, the proposed TL is implemented on an amorphous lattice and does not follow the conventional bulk-boundary correspondence.

Intelligent meta-materials can achieve spatial invisibility for objects. In the field of information, information is invisible, but the characteristics of the signal carrying information change with time. The temporal cloak technique conceals information by selectively opening and closing temporal windows in the time domain, effectively masking data from detection light. However, conventional temporal cloaks relying on dispersion or specialized materials lack optical carriers, making event information undetectable by collaborators—a critical limitation. Our solution employs semiconductor lasers with optical injection, achieving temporal cloak activation through precise control of photon numbers and phase synchronization within the cavity. Furthermore, by utilizing low-risk spontaneous emission light as optical carrier, collaborators can receive data while remaining invisible to non-participants. Moreover, we propose time-frequency coding modulation, which greatly enhances the concealment and anti-interference ability.

Spontaneous Symmetry-Breaking (SSB) is a fascinating and ubiquitous phenomenon, which has been observed in a large variety of physical systems. In optics, a major challenge is the spatio-temporal structuration of light for imaging and computing applications. Recently, the mode-locked VECSEL platform has been exploited for the generation of complex spatio-temporal states consisting of addressable pulses emitted onto symmetric tilted waves (TW) [1]. In this work, we report the observation of the SSB of TWs emitted by a nearly-degenerate mode-locked VECSEL. The SSB manifests as a transition from a symmetric TW emission to a regime where the pulsed emission alternates periodically or irregularly between the +k0 (CW mode) and -k0 (CCW mode). This result demonstrates the potential of degenerate laser systems for the spontaneous generation of novel spatio-temporal structuration of light. [1] A. Bartolo et al., Photonics Research 11, 1751 (2023).

This paper presents the design and characterization of a high-speed, high-spectral-resolution grating spectrometer for a low-cost vertically emitting VCSEL swept-source laser diode for the detection of hydrogen in the 850 nm range. The laser beam is spectrally dispersed using an optical grating, and the resulting intensity profile is recorded in a time-resolved manner using an avalanche photodiode detector (APD) mounted on a linear stage. Periodic variations in wavelength can be detected by recording the intensity signal in a time-resolved manner. In pulsed mode, the system enables the analysis of spectral emission as a function of current and temperature modulations. This allows the investigation of the dynamic tuning behavior of the VCSEL and the optimization of a sawtooth-shaped control signal for fast tuning of the emission spectrum. The developed grating spectrometer achieved a temporal resolution of 20 ns with a spectral resolution of 0.059 nm.

The realization of compact, energy-efficient integrated lasers operating at 1.3 µm remains a key objective in silicon photonics. We present a design-focused numerical study of hybrid III–V/Si distributed Bragg reflector (DBR) lasers, analyzing trade-offs and optimization strategies using supermode theory. We co-optimize the silicon width, bonding-oxide thickness, and III–V stack for a III–V-taper-free hybrid QD DBR laser on 400-nm SOI. Supermode-based design maps and sensitivity analyses reveal tolerance windows that preserve strong III–V gain overlap in the active section and efficient transfer to silicon in the passive sections, while optimized silicon adiabatic tapers minimize coupling into higher-order modes.

Phase resetting is a technique used to investigate how the phase of an oscillating system is altered due to an external perturbation. In this work we investigate the effect of external perturbations on a Q-switched laser, modelled by the Yamada equations. Using a dynamical systems approach, we present phase transition curves (PTCs) for perturbations in the laser intensity and the gain, and show how the phase of the reset oscillations are affected by the size of the perturbation, and the time at which it is applied.

A compact mid-infrared (MIR) cavity-enhanced measurement system for methane trace gas detection was developed using a quantum interband cascade LED (QIC-LED) emitting at 3.3 µm. The system integrates a low-noise indium arsenide (InAs) detector with a 35 nm FWHM narrowband filter and a custom amplifier capable of modulation detection up to 30 kHz. A short coupling distance between the QIC-LED and the cavity mirror increases optical feedback and transmission efficiency while maintaining a compact and mechanically stable geometry. The QIC-LED was driven in pulsed overdrive mode at 30 kHz, providing approximately sixteen times higher peak output power compared to continuous-wave operation while managing thermal load. The narrowband filtering enables precise spectral targeting of the methane absorption feature at 3.315 µm. Initial results show stable, low-noise signal acquisition and effective high-speed modulation, demonstrating strong potential for portable MIR sensing and localized methane emission monitoring.

Efficient heat removal from the active region of a quantum cascade laser (QCL) is crucial for achieving continuous-wave operation, reliability, and higher wall-plug efficiency. This study combines analytical modeling and experimental methods to investigate heat propagation within QCL chips. Using linear response theory, the model predicts both quantitative and qualitative aspects of thermal behavior, showing that variations in QCL design dimensions lead to different heat dissipation regimes. This dimensional transition is used to fit experimental data and describe temperature rise through an analytical function. The effective diffusion constant, which characterizes heat dissipation efficiency, can be determined experimentally by measuring the nonlinear wavelength chirp of Fabry–Perot modes. Tests on QCL samples with varying post-growth processes validate the model and measurement approach, demonstrating that it can identify the most thermally efficient fabrication methods. As a result, a non-invasive technique is proposed for benchmarking QCL thermal efficiency based on overheating dynamics analysis.

We present a multidomain experimental comparison of single-section quantum-dash (QDash) and quantum-well (QWell) passively mode-locked lasers under identical operating and measurement conditions. Their behavior is investigated in both the RF and optical domains as functions of bias current and temperature. Static characterization establishes baseline performance, while RF characterization investigates the repetition frequency and RF linewidth of the beat-note signal and extends to timing jitter and long-term stability. Optical measurements characterize the spectrum in terms of central wavelength, spectral bandwidth, number of modes, and the optical linewidth of individual modes. Several results diverge from previously reported trends, revealing contrasting performance between QDash and QWell devices. The study further examines the effects of short and long external optical feedback on their dynamic behavior.

Recent studies have explored simultaneous transverse and longitudinal modulation of gain and refractive index to improve the beam quality of broad-area semiconductor lasers, which are typically affected by filamentation and broadened far-field profiles. In this work, we propose a combined lateral and longitudinal structuring of the electrode and analyze the resulting beam quality using a comprehensive numerical model. This model captures the temporal and longitudinal evolution of the transverse distributions of both the optical field and carrier density. Within this framework, we demonstrate that appropriately engineered transverse and longitudinal electrode modulation can suppress the far-field side peaks that usually arise when only transverse modulation is applied, while preserving the stability of near-field profiles with respect to current density.

Even after decades of research, active-mode locking continues to draw tremendous attention due to the recent demonstration of novel lasing states. These advancements have been enabled by injecting a microwave signal into a semiconductor laser, which co-propagates together with the optical field along the waveguide of the device. To develop a deeper understanding of the underlying physics in such devices, we present a simplified model that is both accurate as well as efficient. Our approach combines numerical simulations of the optical field and gain medium dynamics with an analytical solution for the microwave propagation. We demonstrate the validity and limitations of our model by simulating real-world devices and comparing our results with those of a general, non-simplified model for microwave-optical co-propagation.

The intensity noise of a laser source represents one of the key factors limiting the ultimate sensitivity in laser-based systems for sensing and limits the signal-to-noise ratio in telecommunication. For advanced applications based on interferometry, the availability of a shot-noise-limited local oscillator is even more important. The intensity noise features of quantum cascade and interband cascade lasers will be presented. A thorough electro-optical characterization was performed, together with a detailed intensity noise analysis.

The recent emergence of quantum technologies in the commercial market brings the challenge of scaling up their production to meet future demands. To this end, it is necessary to establish a supply chain of components with a high technological value that are increasingly affordable, more robust, and simpler to operate. We present a laser module specifically designed to provide a stable and reliable source of coherent light in the visible/IR region for quantum technologies based on atomic, molecular, and optical (AMO) platforms and developed during the EIC project AQLAS (Advanced lasers for quantum technologies). The device integrates a laser source based on a modified Littrow configuration [1,2], an optical frequency discriminator (OFD) as frequency reference, and all necessary electronics within a single 19-inch 3U rack box, delivering a laser beam through an optical fiber ready for applications such as precision spectroscopy and laser cooling. Our first prototype delivers laser light with a linewidth on the order of 10kHz over 1 second and 1MHz over 1.5 hours in a laboratory environment. We illustrate the latest results in the design and characterization of our laser as well as the most recent results obtained applying our device to quantum technologies. [1] L. Duca, E. Perego, F. Berto, C. Sias, "Design of a Littrow-type diode laser with independent control of cavity length and grating rotation" Opt. Lett. 46, 2840 (2021). [2] C. Sias, L. Duca, E. Perego, patents US 12,132,291 B2; JP7457723B2; IT102019000002013.

Dynamic wavelength tuning is essential for advanced photonic systems, yet existing semiconductor laser technologies struggle to combine speed, precision, stability, and compatibility with photonic integration. This work uses dynamic targeting, a feedback-based control technique that enables agile, continuous, and mode-hop–free wavelength tuning by adjusting the external-cavity feedback rate and phase. Originally developed for stabilizing lasers under strong feedback, the method locks the device to the maximum gain mode, allowing smooth and predictable frequency shifts. Recent experiments demonstrate stable tuning over 2.1 GHz, while simulations indicate scalability to tens of gigahertz and ultrafast scan speeds above 10¹⁷ Hz/s. The talk reviews the physical principles, experimental validation, performance limits, and practical integration challenges, highlighting dynamic targeting as a promising pathway toward compact, high-speed, wavelength-agile semiconductor lasers for next-generation photonic circuits.

Self-injection locking (SIL) provides an efficient route to stabilizing semiconductor lasers with narrow linewidth and low phase noise using passive optical feedback from high-Q resonators. In this work, we demonstrate how optical fiber ring cavities assembled from standard telecommunication components can be used to enhance the performance of distributed-feedback (DFB) lasers through SIL. Experimental results show more than four orders of magnitude linewidth narrowing, phase-locked dual-frequency generation based on stimulated Brillouin scattering, controllable tuning of laser coherence over two orders of magnitude, and continuous wavelength tuning over more than 10 GHz via thermal control. These capabilities establish SIL DFB lasers with fiber ring cavities as versatile sources for sensing and microwave photonics.